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    <script>
    var [a=3,b=a,c=3]=[1,2,undefined];
    console.log(a,b,c);//1,2,3
    // 考察的是ES6的解构赋值，等号前面为变量名，等号后面为变量值，他们是一一对应的，后面有值就替换，没值走默认
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